HDO, PDO and CLO are important monomer building blocks, in particular for the preparation of polyesters and polyurethanes. Said substances can be obtained, with the high purity required for the intended use mentioned, preferably of at least 99%, in particular virtually free of 1,4-cyclohexanediol, by a known process described in DE-A 196 07 954, from a complex carboxylic acid mixture which is obtained as a byproduct of the oxidation of cyclohexane to cyclohexanone/cyclohexanol. In the process described in DE 196 07 954, a starting mixture itself generally referred to as dicarboxylic acid solution (DCS), is a complex mixture of a large number of substances. A hydrogenation discharge is obtained therefrom in 5 stages by a multistage process, from which discharge a stream containing predominantly 1,6-hexanediol in addition to 1,5-pentanediol is obtained by distillation in stage 6. A 1,5-pentanediol-containing top stream, from which 1,5-pentanediol is obtained as a pure product by distillation, and a side stream containing 1,6-hexanediol as pure product is taken off therefrom in stage 7 by separation by distillation.
Cyclization of a stream containing predominantly 6-hydroxycaproic esters in stage 13 gives caprolactone, which is worked up in stage 14 by distillation. Owing to the complex mixtures of substances, it was surprising that, in spite of the unfavorable boiling point conditions and risk of azeotrope formation, the target products HDO, PDO and CLO could be obtained by distillation in high purity, in particular HDO with a very small residual 1,4-cyclohexanediol content.
Dividing wall columns, i.e. distillation columns having vertical dividing walls which prevent cross-mixing of liquid streams and vapor streams in certain regions, are known for the separation of multicomponent mixtures by distillation. The dividing wall, which can preferably consist of a metal sheet, divides the middle region of the column in the longitudinal direction into a feed section and a take-off section.
A similar result can be achieved with thermally coupled columns, i.e. arrangements of at least two columns where each of the columns has at least two links with each other column at spatially separate points.